2.1. TNF-α
Tumor necrosis factor alpha (TNF-α) is a cytokine that is released primarily by inflammation and mononuclear phagocytes in response to immunostimulators. TNF-α is capable of enhancing most cellular processes, such as differentiation, recruitment, proliferation, and proteolytic degradation. At low levels, TNF-α confers protection against infective agents, tumors, and tissue damage. However, TNF-α also has role in many diseases. When administered to mammals such as humans, TNF-α causes or aggravates inflammation, fever, cardiovascular effects, hemorrhage, coagulation, and acute phase responses similar to those seen during acute infections and shock states. Enhanced or unregulated TNF-α production has been implicated in a number of diseases and medical conditions, for example, cancers, such as solid tumors and blood-born tumors; heart disease, such as congestive heart failure; and viral, genetic, inflammatory, allergic, and autoimmune diseases.
Cancer is a particularly devastating disease, and increases in blood TNF-α levels are implicated in the risk of and the spreading of cancer. Normally, in healthy subjects, cancer cells fail to survive in the circulatory system, one of the reasons being that the lining of blood vessels acts as a barrier to tumor-cell extravasation. However, increased levels of cytokines have been shown to substantially increase the adhesion of cancer cells to endothelium in vitro. One explanation is that cytokines, such as TNF-α stimulate the biosynthesis and expression of a cell surface receptors called ELAM-1 (endothelial leukocyte adhesion molecule). ELAM-1 is a member of a family of calcium-dependent cell adhesion receptors, known as LEC-CAMs, which includes LECAM-1 and GMP-140. During an inflammatory response, ELAM-1 on endothelial cells functions as a “homing receptor” for leukocytes. ELAM-1 on endothelial cells was shown to mediate the increased adhesion of colon cancer cells to endothelium treated with cytokines (Rice et al., 1989, Science 246:1303–1306).
Inflammatory diseases such as arthritis, related arthritic conditions (e.g., osteoarthritis and rheumatoid arthritis), inflammatory bowel disease, sepsis, psoriasis, chronic obstructive pulmonary diseases and chronic inflammatory pulmonary diseases are also prevalent and problematic ailments. TNF-α plays a central role in the inflammatory response and the administration of their antagonists block chronic and acute responses in animal models of inflammatory disease.
Enhanced or unregulated TNF-α production has been implicated in viral, genetic, inflammatory, allergic, and autoimmune diseases. Examples of such diseases include, but are not limited to: HIV; hepatitis; adult respiratory distress syndrome; bone-resorption diseases; chronic obstructive pulmonary diseases; chronic pulmonary inflammatory diseases; dermatitis; cystic fibrosis; septic shock; sepsis; endotoxic shock; hemodynamic shock; sepsis syndrome; post ischemic reperfusion injury; meningitis; psoriasis; fibrotic disease; cachexia; graft versus host disease (GVHD); graft rejection; auto-immune disease; rheumatoid spondylitis; arthritic conditions, such as rheumatoid arthritis, rheumatoid spondylitis and osteoarthritis; osteoporosis; inflammatory-bowel disease; Crohn's disease; ulcerative colitis; multiple sclerosis; systemic lupus erythrematosus; ENL in leprosy; radiation damage; asthma; and hyperoxic alveolar injury. Tracey et al., 1987, Nature 330:662–664 and Hinshaw et al., 1990, Circ. Shock 30:279–292 (endotoxic shock); Dezube et al., 1990, Lancet, 335:662 (cachexia ); Millar et al., 1989, Lancet 2:712–714 and Ferrai-Baliviera et al., 1989, Arch. Surg. 124:1400–1405 (adult respiratory distress syndrome); Bertolini et al., 1986, Nature 319:516–518, Johnson et al.,1989, Endocrinology 124:1424–1427, Holler et al., 1990, Blood 75:1011–1016, and Grau et al., 1989, N. Engl. J. Med. 320:1586–1591 (bone resorption diseases); Pignet et al., 1990, Nature, 344:245–247, Bissonnette et al., 1989, Inflammation 13:329–339 and Baughman et al., 1990, J. Lab. Clin. Med. 115:36–42 (chronic pulmonary inflammatory diseases); Elliot et al., 1995, Int. J. Pharmac. 17:141–145 (rheumatoid arthritis); von Dullemen et al., 1995, Gastroenterology 109:129–135 (Crohn's disease); Duh et al., 1989, Proc. Nat. Acad. Sci. 86:5974–5978, Poll et al., 1990, Proc. Nat. Acad. Sci. 87:782–785, Monto et al., 1990, Blood 79:2670, Clouse et al., 1989, J. Immunol. 142, 431–438, Poll et al., 1992, AIDS Res. Hum. Retrovirus, 191–197, Poli et al. 1990, Proc. Natl. Acad. Sci. 87:782–784, Folks et al., 1989, Proc. Natl. Acad. Sci. 86:2365–2368 (HIV and opportunistic infections resulting from HIV).
2.2. PDE4
Adenosine 3′,5′-cyclic monophosphate (cAMP) also plays a role in many diseases and conditions, such as, but not limited to asthma and inflammation (Lowe and Cheng, Drugs of the Future, 17(9), 799–807, 1992). It has been shown that the elevation of cAMP in inflammatory leukocytes inhibits their activation and the subsequent release of inflammatory mediators, including TNF-α and nuclear factor κB (NF-κB). Increased levels of cAMP also lead to the relaxation of airway smooth muscle.
It is believed that primary cellular mechanism for the inactivation of cAMP is the breakdown of cAMP by a family of isoenzymes referred to as cyclic nucleotide phosphodiesterases (PDE) (Beavo and Reitsnyder, Trends in Pharm., 11, 150–155, 1990). There are twelve known members of the family of PDEs. It is recognized that the inhibition of PDE type IV (PDE4) is particularly effective in both the inhibition of inflammatory mediated release and the relaxation of airway smooth muscle (Verghese, et al., Journal of Pharmacology and Experimental Therapeutics, 272(3), 1313–1320, 1995). Thus, compounds that specifically inhibit PDE4 may inhibit inflammation and aid the relaxation of airway smooth muscle with a minimum of unwanted side effects, such as cardiovascular or anti-platelet effects.
The PDE4 family that is specific for cAMP is currently the largest and is composed of at least 4 isozymes (a–d), and multiple splice variants (Houslay, M. D. et al. in Advances in Pharmacology 44, eds. J. August et al., p. 225, 1998). There may be over 20 PDE4 isoforms expressed in a cell specific pattern regulated by a number of different promoters. Disease states for which selective PDE4 inhibitors have been sought include: asthma, atopic dermatitis, depression, reperfusion injury, septic shock, toxic shock, endotoxic shock, adult respiratory distress syndrome, autoimmune diabetes, diabetes insipidus, multi-infarct dementia, AIDS, cancer, Crohn's disease, multiple sclerosis, cerebral ischemia, psoriasis, allograft rejection, restenosis, ulceratiave colitis, cachexia, cerebral malaria, allergic rhino-conjunctivitis, osteoarthritis, rheumatoid arthrirtis, chronic obstructive pulmonary disease (COPD), chronic bronchitis, cosinophilic granuloma, and autoimmune encephalomyelitis (Houslay et al., 1998). PDE4 is present in the brain and major inflammatory cells and has been found in abnormally elevated levels in a number of diseases including atopic dermatitis or eczema, asthma, and hay fever among others (reference OHSU flyer and J. of Allergy and Clinical Immunology, 70: 452–457, 1982 by Grewe et al.). In individuals suffering from atopic diseases elevated PDE-4 activity is found in their peripheral blood mononuclear leukocytes, T cells, mast cells, neutrophils and basophils. This increased PDE activity decreases cAMP levels and results in a breakdown of cAMP control in these cells. This results in increased immune responses in the blood and tissues of those that are affected.
Some PDE 4 inhibitors reportedly have a broad spectrum of anti-inflammatory activity, with impressive activity in models of asthma, chronic obstructive pulmonary disorder (COPD) and other allergic disorders such as atopic dermatitis and hay fever. PDE 4 inhibitors that have been used include theophylline, rolipram, denbufylline, ARIFLO, ROFLUMILAST, CDP 840 (a tri-aryl ethane) and CP80633 (a pyrimidone). PDE4 inhibitors have been shown to influence eosinophil responses, decrease basophil histamine release, decrease IgE, PGE2, IL10 synthesis, and decrease anti-CD3 stimulated Il-4 production. Similarly, PDE4 inhibitors have been shown to block neutrophil functions. Neutrophils play a major role in asthma, chronic obstructive pulmonary disorder (COPD) and other allergic disorders. PDE4 inhibitors have been shown to inhibit the release of adhesion molecules, reactive oxygen species, interleukin (IL)-8 and neutrophil elastase, associated with neutrophils which disrupt the architecture of the lung and therefore airway function. PDE4 inhibitors influence multiple functional pathways, act on multiple immune and inflammatory pathways, and influence synthesis or release of numerous immune mediators. J. M. Hanifin and S. C. Chan, “Atopic Dermatitis—Therapeutic Implication for New Phosphodiesterase Inhibitors,” Monocyte Dysregulation of T Cells in AACI News, Jul. 2, 1995; J. M. Hanifin et al., “Type 4 Phosphodiesterase Inhibitors Have clinical and In Vitro Anti-inflammatory Effects in Atopic Dermatitis,” Journal of Investigative Dermatology, 1996, 107, pp51–56).
Some of the first generation of PDE-4 inhibitors are effective in inhibiting PDE4 activity and alleviating a number of the inflammatory problems caused by over expression of this enzyme. However, their effectiveness is limited by side effects, particularly when used systemically, such as nausea and vomiting. Huang et al., Curr. Opin. In Chem. Biol. 2001, 5:432–438. Indeed, all of the PDE-4 inhibitors developed to date have been small molecule compounds with central nervous system and gastrointestinal side effects, e.g., headache, nausea/emesis, and gastric secretion.
2.3. MMP
Matrix metalloproteinases (MMPs) are a family of proteases (enzymes) involved in the degradation and remodeling of connective tissues. Excessive degradation of extracellular matrix by MMPs is implicated in the pathogenesis of many diseases, including rheumatoid arthritis, osteoarthritis, cancer, multiple sclerosis, bone resorptive diseases (such as osteoporosis), chronic obstructive pulmonary disease, restenosis, cerebral hemorrhaging associated with stroke, periodontal disease, aberrant angiogenesis, tumor invasion and metastasis, corneal and gastric ulceration, ulceration of skin, aneurysmal disease, and in complications of diabetes. MMP inhibition is, therefore, recognized as a good target for therapeutic intervention of this type of diseases. Many compounds having MMP inhibition activities have been reported (R. A. Nigel et al, Current Opinion on Therapeutic Patents, Vol. 4, 7–16, (1994), R. P. Beckett et al, Drug Discovery Today, Vol. 1, 16–26, (1996)). However, most are peptide derivatives based on the amino acid sequence of the enzymatic cleavage site in the collagen molecule constituting the substrate of MMP. A need exists for small molecule inhibitors of MMP.